Rabbit immunoglobulin allotypes are antigenic determinants thought to be inherited as autosomal co-dominant alleles. This notion has recently been challenged by observations of low concentrations of allotypes not detected by qualitative tests or predicted by parental genotypes. In the past year, molecules with "latent" allotypes have been isolated from the sera of pedigreed rabbits and shown to be indistinguishable from the normal allotypes. Trivial explanations for these observations, such as cellular chimerism and cross-reactivity of allotypes, have been virtually eliminated by our recent experimentation. Current research focuses on attempts to describe the role of allotypes in control of immunoglobulin genes and on methods to provoke expression of latent allotypes in vitro and in vivo with various mitogens and other pharmacologic agents.